[cfe-dev] Porting libcxxabi / Unwind to Windows / MingW 32 bit

[Yaron Keren]

Hi,

You are exactly correct, LocalAddressSpace::findUnwindSections does nothing
#if !APPLE so the output value is random.

LocalAddressSpace::findOtherFDE and LocalAddressSpace::findFunctionName
also currently do nothing. Are these also required for regular exceptions?

Yaron



2013/10/31 Nick Kledzik <kledzik at apple.com>

> Yaron,
>
> Each separately linked image (program, DLLs, etc) has its own set of FDEs
> (in its .eh_frame) section.  The method
> LocalAddressSpace::findUnwindSections() needs to be updated in an OS
> specific way to: 1) find the image for a given pc value, and 2) find the
> .eh_frame section bounds for that image.
>
> -Nick
>
>
> On Oct 30, 2013, at 3:03 PM, Yaron Keren <yaron.keren at gmail.com> wrote:
>
> Hi Nick,
>
> I looked at the disassembly, unw_getcontext() gets the correct IP into the
> context and later setInfoBasedOnIPRegister gets it right into "pc". This is
> OK.
>
> The trouble is, the whole address space is nowhere near the fde values.
> For example,
>
> p =          0x66179070
> <libunwind::DwarfFDECache<libunwind::LocalAddressSpace>::_initialBuffer>
> pc =         0x6604e7d9
> fde =         0x40801c0
> p->ip_start = 0x4080010
> p->ip_end =   0x408010c
>
> p is consistent with pc and local vars and addresses in unwind.dll
> (0x66YYYYYY)
> fde is consistent with the ip ranges and with the caller of unwind.dll
> (the throwing function) address space (0x40800YY)
>
> they live in different memory ranges, the fde addresses are in caller
> range whereas the unwind addresses are in the DLL range so when it tries to
> find its IP in the fde tables it can't find.
>
> It's as if the DLL is supposed to load in other memory range, some linker
> option required?
>
> Yaron
>
>
>
> 2013/10/29 Nick Kledzik <kledzik at apple.com>
>
>>
>> On Oct 29, 2013, at 12:11 AM, Yaron Keren <yaron.keren at gmail.com> wrote:
>>
>> > Hello,
>> >
>> > I'm trying to make libcxxabi / Unwind work on Windows / MingW 32 bit.
>> Attached is a patch to make it compile without warnings and run without
>> crashing.
>> >
>> > However the functionality isn't working yet: upon exception, the IP
>> seems to be completely out of range the FDE tables. This may be related to
>> the memory model / compilation options???
>> Take a look at UnwindRegisterRestore.s.  When an exception is thrown,
>> unw_getcontext() is called which saves all registers and the return address
>> into a register struct.  Then the FDE info is used to step through each
>> frame and modify the register set.  At which step is the IP register out of
>> bounds?
>>
>> It might be that the C files need to be compiled with -fexceptions so
>> that they have unwind tables.
>>
>> -Nick
>>
>>
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20131031/67eedc94/attachment.html>